A magnetically permeable rotor for an electric machine and a method of manufacturing the same

Abstract

The application discloses a motor magnetic rotor and a preparation method thereof. Stearic acid and its derivatives are prone to migrate from a resin matrix to a material surface to form precipitates. If the micro motor product surface appears the precipitates, the rotor rotation condition and precision are affected, and the rotor is seriously stuck to cause product failure. In the preparation process of the motor magnetic rotor, the raw material magnetic powder is prepared by the following method: amino terminal coupling agent solution and magnetic powder are mixed, the amino terminal coupling agent is coated on the surface of the magnetic powder, and the -NH2 functionalized magnetic powder is obtained by drying; the stearic acid solution is mixed with the -NH2 functionalized magnetic powder, a dehydrating agent is added at room temperature for reaction, and the product is filtered and dried to obtain the modified magnetic powder grafted with the stearic acid. The stearic acid is combined to the surface of the magnetic powder particles in the form of a chemical bond, the migration of the stearic acid from the material over time is effectively inhibited, material degradation and product surface pollution are avoided, and the filling amount of the magnetic filler is effectively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of motor magnetic rotors and relates to a motor magnetic rotor and a preparation method thereof. BACKGROUND

[0002] With the rapid development of new energy vehicles in recent years, the application of vehicle thermal management systems is also becoming more and more widespread. Key components such as electronic expansion valves, water valves, electronic water pumps and oil pumps driven by micro-motors are key components of motor magnetic rotors. With increasingly stringent requirements for products, the corresponding magnetic rotors also face higher performance requirements.

[0003] Stearic acid and its derivatives are a commonly used plastic processing aid. Due to its excellent lubricating performance, it can effectively improve the problems such as rough surface of the product, difficult demolding and the like. However, stearic acid and its derivatives have a significant defect, that is, they are small molecules and can easily migrate from the resin matrix to the surface of the material to form precipitates, which pollute the surface appearance of the product. At the same time, with the loss of stearic acid and its derivatives, the performance of the material will gradually deteriorate and lose its value. For micro-motor products, if precipitates appear on the surface of the product, it may also affect the rotation and precision of the rotor, and in severe cases, it may also cause the rotor to be stuck and thus cause product failure. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art and provide a motor magnetic rotor and a preparation method thereof, which can effectively inhibit the migration of stearic acid from the material over time, thereby avoiding material degradation, product surface pollution and other problems.

[0005] In a first aspect, the present application provides a preparation method of a motor magnetic rotor, wherein the magnetic powder is prepared by the following steps:

[0006] An amino-terminal coupling agent is added to a mixture of water and ethanol to hydrolyze and obtain an amino-terminal coupling agent solution;

[0007] The magnetic powder is added to the amino-terminal coupling agent solution for mixing, so that the amino-terminal coupling agent is coated on the surface of the magnetic powder, and then dried to obtain the -NH2 functionalized magnetic powder;

[0008] Stearic acid is dissolved in a solvent to obtain a stearic acid solution;

[0009] The stearic acid solution and the -NH2 functionalized magnetic powder are mixed, a dehydrating agent is added and reacted at room temperature, and then the product is filtered and dried to obtain the modified magnetic powder grafted with stearic acid.

[0010] In a second aspect, the present application provides a motor magnetic rotor prepared by the above method.

[0011] The stearic acid is uniformly combined to the surface of the magnetic powder particles in the form of chemical bond, effectively inhibits the stearic acid from migrating out of the material over time, thereby avoiding problems such as material degradation, product surface contamination, and the like, and also effectively improves the filling amount of the magnetic filler (i.e., the magnetic powder). BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 A process route map for grafting stearic acid to the surface of the magnetic powder in the present application.

[0013] Figure 2 A process route map for Comparative Examples 1-2. DETAILED DESCRIPTION

[0014] As described previously, in view of the deficiencies of the prior art, the present inventors, after long-term research and a large number of practices, proposed the technical solution of the present application, which is mainly based on at least the following: the present application uniformly combines stearic acid to the surface of the magnetic powder particles in the form of chemical bond by means of chemical bond combination, which on the one hand can effectively improve the flowability of the plastic magnetic material, and on the other hand can effectively avoid the migration behavior of stearic acid, so that the material performance will not be significantly degraded over time, and the surface of the micro motor rotor will not be contaminated by the precipitates to affect the rotation; at the same time, the stearic acid layer on the surface of the magnetic powder can effectively reduce the friction between the powder particles, which is beneficial to the rotational orientation of the magnetic powder, so that the material can maintain high orientation degree under different filling amounts of the magnetic powder, effectively improving the problem of difficult orientation of the magnetic powder in the high filling system, thereby further improving the magnetic performance of the motor magnetic rotor.

[0015] The present application discloses a specific embodiment, a motor magnetic rotor and a preparation method thereof.

[0016] The method comprises the following steps:

[0017] Step 1, preparation of modified magnetic powder

[0018] The amino-terminated coupling agent is added to a mixture of water and ethanol to hydrolyze, obtaining an amino-terminated coupling agent solution;

[0019] The magnetic powder is added to the amino-terminated coupling agent solution for mixing, so that the amino-terminated coupling agent is coated on the surface of the magnetic powder, and the -NH2 functionalized magnetic powder is obtained by drying in a vacuum oven at 70-100℃;

[0020] The stearic acid is dissolved in a solvent (such as chloroform, DMF, DMSO) to obtain a stearic acid solution;

[0021] The stearic acid solution is mixed with the -NH2 functionalized magnetic powder, a dehydrating agent is added, and the reaction is carried out at room temperature, and the product is filtered and dried to obtain the stearic acid grafted modified magnetic powder.

[0022] The mass ratio of the magnetic powder, the amino-terminal coupling agent and the stearic acid is 100:(0.2-2):(0.2-2); the mass ratio of the stearic acid and the dehydrating agent is 100:(0.2-2).

[0023] Further, the magnetic powder is one or more mixtures of neodymium iron boron, samarium iron nitride, ferrite, samarium cobalt and aluminum-nickel-cobalt. The amino-terminal coupling agent is one or a mixture of both of the following: aminopropyltriethoxysilane and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane. The dehydrating agent is one or more mixtures of dicyclohexyl carbodiimide, 4-dimethylaminopyridine and hexamethyldisilyl lithium.

[0024] Another embodiment of the present application is disclosed, and further comprises mixing and granulating the magnetic powder and the resin:

[0025] The modified magnetic powder, the resin and the composite additive are mixed by a high-speed mixer at a mass ratio of (80-95):(5-20):(0.5-2) to obtain a magnetic powder-resin mixture;

[0026] The magnetic powder-resin mixture is granulated by a double-screw extruder at 210-320 DEG C to obtain an injection-molded magnet granulate;

[0027] Further, the resin is any one or a mixture of more than one of the following: nylon (PA6, PA11, PA12, PA66, PA612) and polyphenylene sulfide (PPS). The composite additive is a mixture of an antioxidant and a toughening agent.

[0028] Another embodiment of the present application is disclosed, and further comprises injection molding of a motor magnetic rotor

[0029] The injection-molded magnet granulate is injection molded by a magnetic field injection molding machine at 210-320 DEG C to obtain a motor magnetic rotor.

[0030] The orientation magnetic field of the magnetic field injection molding machine is 0.5-2T, and the mold temperature is 40-150 DEG C. More preferably, if the resin is nylon (PA6, PA11, PA12, PA66, PA612), the mold temperature is 40-100 DEG C; if the resin is PPS, the mold temperature is 90-150 DEG C.

[0031] The technical solutions of the present application are further explained and described below in combination with several preferred embodiments, but the experimental conditions and the set parameters therein should not be regarded as limitations on the basic technical solutions of the present application. The protection scope of the present application is not limited to the following examples.

[0032] Example 1

[0033] Step 1: Dissolve 5g of aminopropyltriethoxysilane in 100mL of anhydrous ethanol, add 1mL of deionized water and stir. Add 1000g of samarium iron nitrogen magnetic powder and stir. Dry the reaction mixture in a vacuum oven at 80℃ to obtain -NH2-functionalized samarium iron nitrogen magnetic powder. Dissolve 5g of stearic acid in 500mL of LMF solvent and mix it with the -NH2-functionalized samarium iron nitrogen magnetic powder. Add 0.5g of the dehydrating agent dicyclohexylcarbodiimide and react at 25℃ for 24h. Filter the product and dry it in a vacuum oven at 80℃ to obtain stearic acid-grafted modified magnetic powder.

[0034] Step 2: Take 900g of stearic acid-grafted modified magnetic powder, 90g of PA11 resin and 10g of composite additive (the mass ratio of antioxidant 1010 to elastomer POE is 1:9) and mix them in a high-speed mixer; granulate the mixed magnetic powder / resin mixture at 210℃ using a twin-screw extruder to obtain injection-molded magnetic granules.

[0035] Step 3: The injection-molded magnetic granules were injection molded into a motor magnetic rotor and standard test samples using a magnetic field injection molding machine. The heating section temperature of the injection molding machine was 240℃, the orientation magnetic field was 1.0T, and the mold temperature was 70℃. Melt index, magnetic properties, and surface magnetic properties were tested according to standards such as GB / T3682-2000 and GB / T3217-2013. The rotor was placed in a 90℃ oven for 48 hours, and the sample surface was wiped with oil-absorbing paper to observe whether there were oil traces on the paper to determine the stearic acid precipitation. The results are shown in Table 1 below.

[0036] Example 2

[0037] Step 1: Dissolve 10g of aminopropyltriethoxysilane in 100mL of anhydrous ethanol, add 1mL of deionized water and stir. Add 1000g of samarium iron nitrogen magnetic powder and stir. Dry the reaction mixture in a vacuum oven at 80℃ to obtain -NH2-functionalized samarium iron nitrogen magnetic powder. Dissolve 10g of stearic acid in 500mL of LMF solvent and mix it with the -NH2-functionalized samarium iron nitrogen magnetic powder. Add 1g of the dehydrating agent dicyclohexylcarbodiimide and react at 25℃ for 24h. Filter the product and dry it in a vacuum oven at 80℃ to obtain stearic acid-grafted modified magnetic powder.

[0038] Step 2: Take 900g of stearic acid-grafted modified magnetic powder, 90g of PA11 resin and 10g of composite additive (the mass ratio of antioxidant 1010 to elastomer POE is 1:9) and mix them in a high-speed mixer; granulate the mixed magnetic powder / resin mixture at 210℃ using a twin-screw extruder to obtain injection-molded magnetic granules.

[0039] Step 3: The injection-molded magnetic granules were injection molded into a motor magnetic rotor and standard test samples using a magnetic field injection molding machine. The heating section temperature of the injection molding machine was 240℃, the orientation magnetic field was 1.0T, and the mold temperature was 70℃. Melt index, magnetic properties, and surface magnetic properties were tested according to standards such as GB / T3682-2000 and GB / T3217-2013. The rotor was placed in a 90℃ oven for 48 hours, and the sample surface was wiped with oil-absorbing paper to observe whether there were oil traces on the paper to determine the stearic acid precipitation. The results are shown in Table 1 below.

[0040] Comparative Example 1: One-step physical mixing of magnetic powder, coupling agent and stearic acid

[0041] Step 1: Mix 10g of aminopropyltriethoxysilane, 10g of stearic acid and 1000g of samarium iron nitrogen magnetic powder using a high-speed mixer to obtain modified magnetic powder.

[0042] Step 2: Take 900g of modified magnetic powder, 90g of PA11 resin and 10g of composite additive (the mass ratio of antioxidant 1010 to elastomer POE is 1:9) and mix them in a high-speed mixer; granulate the mixed magnetic powder / resin mixture at 210℃ using a twin-screw extruder to obtain injection-molded magnetic granules.

[0043] Step 3: The injection-molded magnetic granules were injection molded into a motor magnetic rotor and standard test samples using a magnetic field injection molding machine. The heating section temperature of the injection molding machine was 240℃, the orientation magnetic field was 1.0T, and the mold temperature was 70℃. Melt index, magnetic properties, and surface magnetic properties were tested according to standards such as GB / T3682-2000 and GB / T3217-2013. The rotor was placed in a 90℃ oven for 48 hours, and the sample surface was wiped with oil-absorbing paper to observe whether there were oil traces on the paper to determine the stearic acid precipitation. The results are shown in Table 1 below.

[0044] Comparative Example 2: Magnetic powder was treated with only coupling agent and stearic acid, without adding dehydrating agent.

[0045] Step 1: Dissolve 10g of aminopropyltriethoxysilane in 100mL of anhydrous ethanol, add 1mL of deionized water and stir, add 1000g of samarium iron nitrogen magnetic powder and stir, dry the reaction mixture in a vacuum oven at 80℃ to obtain -NH2-functionalized samarium iron nitrogen magnetic powder.

[0046] 10g of stearic acid was dissolved in 500ml of LDM solvent and mixed with -NH2-functionalized samarium iron nitrogen magnetic powder. The mixture was kept at 25°C for 24 hours. The product was filtered and dried in a vacuum oven at 80°C to obtain the modified magnetic powder.

[0047] Step 2: Take 900g of modified magnetic powder, 90g of PA11 resin and 10g of composite additive (the mass ratio of antioxidant 1010 to elastomer POE is 1:9) and mix them in a high-speed mixer; granulate the mixed magnetic powder / resin mixture at 210℃ using a twin-screw extruder to obtain injection-molded magnetic granules.

[0048] Step 3: The injection-molded magnetic granules were injection molded into a motor magnetic rotor and standard test samples using a magnetic field injection molding machine. The heating section temperature of the injection molding machine was 240℃, the orientation magnetic field was 1.0T, and the mold temperature was 70℃. Melt index, magnetic properties, and surface magnetic properties were tested according to standards such as GB / T3682-2000 and GB / T3217-2013. The rotor was placed in a 90℃ oven for 48 hours, and the sample surface was wiped with oil-absorbing paper to observe whether there were oil traces on the paper to determine the stearic acid precipitation. The results are shown in Table 1 below.

[0049] Comparative Example 3: Magnetic powder was treated with only stearic acid and a dehydrating agent, without the addition of a coupling agent.

[0050] Step 1: Dissolve 10g of stearic acid in 500ml of LMF solvent, add 1000g of samarium iron nitrogen magnetic powder and stir, add 1g of dehydrating agent dicyclohexylcarbodiimide and keep at 25℃ for 24h, filter the product and dry it in a vacuum oven at 80℃ to obtain modified magnetic powder.

[0051] Step 2: Take 900g of modified magnetic powder, 90g of PA11 resin and 10g of composite additive (the mass ratio of antioxidant 1010 to elastomer POE is 1:9) and mix them in a high-speed mixer; granulate the mixed magnetic powder / resin mixture at 210℃ using a twin-screw extruder to obtain injection-molded magnetic granules.

[0052] Step 3: The injection-molded magnetic granules were injection molded into a motor magnetic rotor and standard test samples using a magnetic field injection molding machine. The heating section temperature of the injection molding machine was 240℃, the orientation magnetic field was 1.0T, and the mold temperature was 70℃. Melt index, magnetic properties, and surface magnetic properties were tested according to standards such as GB / T3682-2000 and GB / T3217-2013. The rotor was placed in a 90℃ oven for 48 hours, and the sample surface was wiped with oil-absorbing paper to observe whether there were oil traces on the paper to determine the stearic acid precipitation. The results are shown in Table 1 below.

[0053] Comparative Example 4: Magnetic powder was treated with only coupling agent and dehydrating agent, without the addition of stearic acid.

[0054] Step 1: Dissolve 10g of aminopropyltriethoxysilane in 100mL of anhydrous ethanol, add 1mL of deionized water and stir. Add 1000g of samarium iron nitrogen magnetic powder and stir. Dry the reaction mixture in a vacuum oven at 80℃ to obtain -NH2-functionalized samarium iron nitrogen magnetic powder. Mix the -NH2-functionalized samarium iron nitrogen magnetic powder with 500mL of LDM solvent, add 1g of dehydrating agent dicyclohexylcarbodiimide and maintain at 25℃ for 24h. Filter the product and dry it in a vacuum oven at 80℃ to obtain modified magnetic powder.

[0055] Step 2: Take 900g of modified magnetic powder, 90g of PA11 resin and 10g of composite additive (the mass ratio of antioxidant 1010 to elastomer POE is 1:9) and mix them in a high-speed mixer; granulate the mixed magnetic powder / resin mixture at 210℃ using a twin-screw extruder to obtain injection-molded magnetic granules.

[0056] Step 3: The injection-molded magnetic granules were injection molded into a motor magnetic rotor and standard test samples using a magnetic field injection molding machine. The heating section temperature of the injection molding machine was 240℃, the orientation magnetic field was 1.0T, and the mold temperature was 70℃. Melt index, magnetic properties, and surface magnetic properties were tested according to standards such as GB / T3682-2000 and GB / T3217-2013. The rotor was placed in a 90℃ oven for 48 hours, and the sample surface was wiped with oil-absorbing paper to observe whether there were oil traces on the paper to determine the stearic acid precipitation. The results are shown in Table 1 below.

[0057] Comparative Example 5: No surface treatment of magnetic powder

[0058] Take 900g of samarium iron nitrogen magnetic powder, 90g of PA11 resin and 10g of composite additive (the mass ratio of antioxidant 1010 to elastomer POE is 1:9) and mix them in a high-speed mixer; granulate the mixed magnetic powder / resin mixture at 210℃ using a twin-screw extruder to obtain injection-molded magnetic granules.

[0059] The injection-molded magnetic granules were injection molded into a magnetic rotor for a motor and standard test samples using a magnetic field injection molding machine. The heating section temperature of the injection molding machine was 240℃, the orientation magnetic field was 1.0T, and the mold temperature was 70℃. Melt index, magnetic properties, and surface magnetic properties were tested according to standards such as GB / T3682-2000 and GB / T3217-2013. The rotor was placed in a 90℃ oven for 48 hours, and the sample surface was wiped with oil-absorbing paper to observe whether there were oil traces on the paper to determine the stearic acid precipitation. The results are shown in Table 1 below.

[0060] Example 3.

[0061] Step 1: Dissolve 20g of aminopropyltriethoxysilane in 100mL of anhydrous ethanol, add 1mL of deionized water and stir. Add 1000g of samarium iron nitrogen magnetic powder and stir. Dry the reaction mixture in a vacuum oven at 80℃ to obtain -NH2-functionalized samarium iron nitrogen magnetic powder. Dissolve 20g of stearic acid in 500mL of LMF solvent and mix it with the -NH2-functionalized samarium iron nitrogen magnetic powder. Add 2g of the dehydrating agent dicyclohexylcarbodiimide and react at 25℃ for 24h. Filter the product and dry it in a vacuum oven at 80℃ to obtain stearic acid-grafted modified magnetic powder.

[0062] Step 2: Take 900g of stearic acid-grafted modified magnetic powder, 90g of PA11 resin and 10g of composite additive (the mass ratio of antioxidant 1010 to elastomer POE is 1:9) and mix them in a high-speed mixer; granulate the mixed magnetic powder / resin mixture at 210℃ using a twin-screw extruder to obtain injection-molded magnetic granules.

[0063] Step 3: The injection-molded magnetic granules were injection molded into a motor magnetic rotor and standard test samples using a magnetic field injection molding machine. The heating section temperature of the injection molding machine was 240℃, the orientation magnetic field was 1.0T, and the mold temperature was 70℃. Melt index, magnetic properties, and surface magnetic properties were tested according to standards such as GB / T3682-2000 and GB / T3217-2013. The rotor was placed in a 90℃ oven for 48 hours, and the sample surface was wiped with oil-absorbing paper to observe whether there were oil traces on the paper to determine the stearic acid precipitation. The results are shown in Table 1 below.

[0064] Example 4.

[0065] Step 1: Dissolve 30g of aminopropyltriethoxysilane in 100mL of anhydrous ethanol, add 1mL of deionized water and stir. Add 1000g of samarium iron nitrogen magnetic powder and stir. Dry the reaction mixture in a vacuum oven at 80℃ to obtain -NH2-functionalized samarium iron nitrogen magnetic powder. Dissolve 30g of stearic acid in 500mL of LMF solvent and mix it with the -NH2-functionalized samarium iron nitrogen magnetic powder. Add 3g of the dehydrating agent dicyclohexylcarbodiimide and react at 25℃ for 24h. Filter the product and dry it in a vacuum oven at 80℃ to obtain stearic acid-grafted modified magnetic powder.

[0066] Step 2: Take 900g of stearic acid-grafted modified magnetic powder, 90g of PA11 resin and 10g of composite additive (the mass ratio of antioxidant 1010 to elastomer POE is 1:9) and mix them in a high-speed mixer; granulate the mixed magnetic powder / resin mixture at 210℃ using a twin-screw extruder to obtain injection-molded magnetic granules.

[0067] Step 3: The injection-molded magnetic granules were injection molded into a motor magnetic rotor and standard test samples using a magnetic field injection molding machine. The heating section temperature of the injection molding machine was 240℃, the orientation magnetic field was 1.0T, and the mold temperature was 70℃. Melt index, magnetic properties, and surface magnetic properties were tested according to standards such as GB / T3682-2000 and GB / T3217-2013. The rotor was placed in a 90℃ oven for 48 hours, and the sample surface was wiped with oil-absorbing paper to observe whether there were oil traces on the paper to determine the stearic acid precipitation. The results are shown in Table 1 below.

[0068] Example 5: PPS matrix

[0069] Step 1: Dissolve 10g of aminopropyltriethoxysilane in 100mL of anhydrous ethanol, add 1mL of deionized water and stir. Add 1000g of samarium iron nitrogen magnetic powder and stir. Dry the reaction mixture in a vacuum oven at 80℃ to obtain -NH2-functionalized samarium iron nitrogen magnetic powder. Dissolve 10g of stearic acid in 500mL of LMF solvent and mix it with the -NH2-functionalized samarium iron nitrogen magnetic powder. Add 1g of the dehydrating agent dicyclohexylcarbodiimide and react at 25℃ for 24h. Filter the product and dry it in a vacuum oven at 80℃ to obtain stearic acid-grafted modified magnetic powder.

[0070] Step 2: Take 900g of stearic acid-grafted modified magnetic powder, 90g of PPS resin and 10g of composite additive (the mass ratio of antioxidant 1010 to elastomer POE is 1:9) and mix them in a high-speed mixer; granulate the mixed magnetic powder / resin mixture in a twin-screw extruder at 300℃ to obtain injection-molded magnetic granules.

[0071] Step 3: The injection-molded magnetic granules were injection molded into a motor magnetic rotor and standard test samples using a magnetic field injection molding machine. The heating section temperature of the injection molding machine was 310℃, the orientation magnetic field was 1.0T, and the mold temperature was 100℃. Melt index, magnetic properties, and surface magnetic properties were tested according to standards such as GB / T3682-2000 and GB / T3217-2013. The rotor was placed in a 90℃ oven for 48 hours, and the sample surface was wiped with oil-absorbing paper to observe whether there were oil traces on the paper to determine the stearic acid precipitation. The results are shown in Table 1 below.

[0072] Comparative Example 5: PPS matrix, magnetic powder treated only with coupling agent and stearic acid, without adding dehydrating agent.

[0073] Step 1: Dissolve 10g of aminopropyltriethoxysilane in 100mL of anhydrous ethanol, add 1mL of deionized water and stir. Add 1000g of samarium iron nitrogen magnetic powder and stir. Dry the reaction mixture in a vacuum oven at 80℃ to obtain -NH2-functionalized samarium iron nitrogen magnetic powder. Dissolve 10g of stearic acid in 500mL of LMF solvent and mix it with the -NH2-functionalized samarium iron nitrogen magnetic powder. Maintain the mixture at 25℃ for 24h. Filter the product and dry it in a vacuum oven at 80℃ to obtain modified magnetic powder.

[0074] Step 2: Take 900g of modified magnetic powder, 90g of PPS resin and 10g of composite additive (the mass ratio of antioxidant 1010 to elastomer POE is 1:9) and mix them in a high-speed mixer; granulate the mixed magnetic powder / resin mixture in a twin-screw extruder at 300℃ to obtain injection-molded magnetic granules.

[0075] Step 3: The injection-molded magnetic granules were injection molded into a motor magnetic rotor and standard test samples using a magnetic field injection molding machine. The heating section temperature of the injection molding machine was 310℃, the orientation magnetic field was 1.0T, and the mold temperature was 100℃. Melt index, magnetic properties, and surface magnetic properties were tested according to standards such as GB / T3682-2000 and GB / T3217-2013. The rotor was placed in a 90℃ oven for 48 hours, and the sample surface was wiped with oil-absorbing paper to observe whether there were oil traces on the paper to determine the stearic acid precipitation. The results are shown in Table 1 below.

[0076] Table 1. Formulation ratios and test results in each embodiment.

[0077]

[0078]

[0079] ◎: No precipitation X: Precipitation present / : No stearic acid in the sample

[0080] The process routes for Examples 1-5 are shown below. Figure 1 The process routes for Comparative Examples 1-2 are shown below. Figure 2 .

[0081] The above results indicate that grafting stearic acid onto the surface of magnetic powder particles through chemical bonding can effectively improve the processability of injection-molded magnet materials. The results of Examples 1, 2, and 3 show that within a reasonable range, as the content of coupling agent and stearic acid increases, the material's fluidity gradually improves, and its magnetic properties also increase. This indicates that the grafted stearic acid layer on the magnetic powder surface can effectively improve the magnetic powder orientation and enhance the material's magnetic properties. Simultaneously, no precipitates appeared on the surface of the motor's magnetic rotor after high-temperature treatment, indicating that chemical grafting can effectively improve the migration behavior of stearic acid. The results of Comparative Examples 1, 2, 3, 4, and 5 show that when stearic acid is not chemically bonded to the magnetic powder surface, it can play a certain lubricating role in the plastic-magnetic material, but it will significantly precipitate during use, contaminating the product surface.

[0082] It should be noted that the components of the materials and the above embodiments are not intended to limit the present invention. The present invention is not limited to the above embodiments. Any material that meets the requirements of the present invention is within the scope of protection of the present invention.

Claims

1. A method for preparing a magnetic rotor for an electric motor, characterized in that, The magnetic powder is prepared using the following steps: The amino-terminal coupling agent is added to a mixture of water and ethanol for hydrolysis to obtain an amino-terminal coupling agent solution; Magnetic powder is added to the amino-terminal coupling agent solution and mixed to coat the surface of the magnetic powder with the amino-terminal coupling agent. The mixture is then dried to obtain -NH2-functionalized magnetic powder. Stearic acid is dissolved in a solvent to obtain a stearic acid solution; Stearic acid solution was mixed with -NH2 functionalized magnetic powder, a dehydrating agent was added and reacted at room temperature, the product was filtered and dried to obtain stearic acid-grafted modified magnetic powder; the stearic acid-grafted modified magnetic powder is stearic acid uniformly bonded to the surface of magnetic powder particles through chemical bonds; the dehydrating agent is dicyclohexylcarbodiimide.

2. The method according to claim 1, characterized in that, It also includes the following steps: Modified magnetic powder, resin, and composite additives are mixed using a high-speed mixer to obtain a magnetic powder-resin mixture. The magnetic powder-resin mixture is granulated using a twin-screw extruder at 210℃~320℃ to obtain injection-molded magnet granules.

3. The method according to claim 2, characterized in that, It also includes the following steps: The magnetic rotor of the motor is obtained by injection molding magnetic granules at 210℃~320℃ using a magnetic field injection molding machine.

4. The method according to any one of claims 1-3, characterized in that, The mass ratio of the magnetic powder, amino-terminated coupling agent, and stearic acid is 100:(0.2-2):(0.2-2); the mass ratio of stearic acid to dehydrating agent is 100:(0.2-2); the drying conditions in the process of "drying to obtain -NH2-functionalized magnetic powder" are drying in a vacuum oven at 70-100℃; the solvent in the stearic acid solution is one of chloroform, DMF, and DMSO.

5. The method according to any one of claims 1-3, characterized in that, The magnetic powder is one or more of neodymium iron boron, samarium iron nitrogen, ferrite, samarium cobalt, and alnico cobalt; the amino-terminal coupling agent is one or a mixture of two of aminopropyltriethoxysilane and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane.

6. The method according to claim 2, characterized in that, The mass ratio of the modified magnetic powder, resin, and composite additive is (80-95):(5-20):(0.5-2).

7. The method according to claim 2 or 6, characterized in that, The resin is any one or a mixture of nylon PA6, nylon PA11, nylon PA12, nylon PA66, nylon PA612, and polyphenylene sulfide (PPS); the composite additive is a mixture of antioxidants and toughening agents.

8. The method according to claim 3, characterized in that, The orientation magnetic field of the magnetic injection molding machine is 0.5T to 2T, and the mold temperature is 40℃ to 150℃.

9. A magnetic rotor for an electric motor, prepared by the method according to any one of claims 1-8.

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